Thin monolithic slow-release devices for optimum in-package preservation of export table grape varieties

["Table grapes -- Preservation -- Packaging", "Grapes -- Postharvest technology -- South Africa", "Sulfur dioxide", "Botrytis cinerea -- Control", "Coating processes", "Dissertations -- Food science", "Uvasys SO2 sheet"]

Opperman, Willem Jacobus ; Sanderson, R. D.

Stellenbosch University

Others  :  https://scholar.sun.ac.za:443/bitstream/10019.1/53189/1/opperman_thin_2002.pdf

瑞士|英语

来源: Stellenbosch University

【 摘 要 】

ENGLISH ABSTRACT: Prototypes of a new polymer S02 gas-generating sheet for the controlof Botrytis cinerea during the post-harvest storage of table grapes, weredeveloped and manufactured for evaluation using a pilot scale productionplant. Attention was paid to the appearance of the sheet, in order to make ittechnologically efficient as well as aesthetically acceptable to both industry andconsumers.The storage quality of semi-commercial export consignments of variouscultivars table grapes packed with the monolithic thin-film polymer S02 slowrelease sheet, was evaluated and compared to results obtained using thelocally manufactured Uvasys S02 sheet. The following were investigated: theefficacy of the new polymer sheets in controlling storage decay, the stage atwhich S02 damage is manifested on table grapes, the level of S02 damageassociated with different S02 concentrations, whether S02 damage ismanifested more readily at a particular position on the bunch, and the possibleeffect of an increase in storage temperature, from an initial storage at -O.5°Cto 10°C, on the levels of S02 bleaching.Results showed that the new polymer S02 sheet compared favourablywith the existing, commercially available Uvasys S02 sheets. The exact S02concentration required for effective decay control varied for different cultivars,as well as for the different types of grape packages. The S02 concentrationincorporated within the sheet was shown to be lower for grapes packed innon-perforated bags, and slightly higher for those in perforated bags.Differences between cultivars occurred with regard to the level of control andthe levels of S02 damage. Levels of S02 damage were also significantlyaffected by the storage period and temperature fluctuations. No significantdifferences in the levels of decay development and S02 damage wereobserved in relation to the orientation of the bunches in the carton.The extent of damage incurred to grape tissue by the absorption ofS02 gas was determined by low-temperature scanning (LTSEM) andtransmission electron microscopy (TEM) techniques. LTSEM and TEMmicrographs of areas damaged by S02 gas revealed that exposure to S02gas may lead to plasmolysis and the loss of cellular fluids. Although damageto the cell walls, cell wall structures and cell membranes, caused by S02 gas,was more prominent in the tissue layers nearer to the fruit surface, damagealso occurred to a lesser extent in deeper tissue layers.S02 gas release-rate studies of polymer S02 sheets containingvarious concentrations Na2S205 revealed that levels of S02 gas emitteddepended largely on the levels of Na2S205 incorporated into the sheets.Higher levels of S02 gas were released with the polymer sheets of higherconcentrations Na2S205. The release curve for the commercial Uvasys S02sheet was very different to that of the polymer sheets, with much higher levelsof S02 gas emitted initially by the Uvasys S02 sheet compared to the polymersheets, while the polymer sheets emitted low levels of S02 gas for longerperiods compared to the Uvasys S02 sheet.The manufacturing process and the pilot scale production plant thatwas developed and constructed was successfully used to manufacturepolymer S02 generating sheets that are technically sound and efficient, andaesthetically acceptable to industry. The efficacy of such sheets, regardinglevels of decay control and S02 damage, was similar to that obtained with thepresently available, commercially used Uvasys S02 sheet.